Final answer:
Two types of emulsions are oil-in-water (O/W) and water-in-oil (W/O), with O/W being more common due to its cosmetic acceptability and ease of washing off. W/O emulsions provide better moisturizing benefits. Emulsifying agents are essential for the stability of emulsions to prevent separation.
Step-by-step explanation:
Types of Emulsions and Their Properties
Emulsions are mixtures of two immiscible liquids where one is dispersed in the other in the form of droplets. The two main types of emulsions are oil-in-water (O/W) and water-in-oil (W/O). In an O/W emulsion, oil droplets are dispersed in water, which is the external phase. Conversely, in a W/O emulsion, water droplets are dispersed in oil, forming the external phase. O/W emulsions are more common and preferred cosmetically as they are less greasy and can be washed off with water. They are widely used in lotions and milk, where substances like cetearyl alcohol or casein act as emulsifying agents to maintain stability. W/O emulsions are typically more moisturizing and provide an oily barrier that helps to reduce water loss from the skin, making them more suitable for creams that are meant to hydrate. These emulsions are more complex to create and handle because they are greasier and not easily washed off with water.
Emulsifying agents are critical for stabilizing emulsions, preventing the dispersed phase from coalescing. Examples include soap, which stabilizes kerosene in water, and egg yolk, which emulsifies oil in vinegar for making mayonnaise.